Foundations of Vibroacoustics

Colin Hansen

• Publisher: CRC Press
• Year: 2018
• ISBN:
  9781351600262
• Edition: 1
• Topic: Tecnologia e ingegneria
• Subtopic: Ingegneria acustica

This text provides the foundation material for solving problems in vibroacoustics. These include the prediction of structural vibration levels and sound pressure levels in enclosed spaces resulting from known force or acoustic pressure excitations and the prediction of sound levels radiated by vibrating structures. The book also provides an excellent theoretical basis for understanding the processes involved in software that predicts structural vibration levels and structural sound radiation resulting from force excitation of the structure, as well as sound levels in enclosed spaces resulting from vibration of part of the enclosing structure or resulting from acoustic sources within the enclosure.

The book is written in an easy to understand style with detailed explanations of important concepts. It begins with fundamental concepts in vibroacoustics and provides a framework for problem solution in both low and high frequency ranges. It forms a primer for students, and for those already well versed in vibroacoustics, the book provides an extremely useful reference. It offers a unified treatment of both acoustics and vibration fundamentals to provide a basis for solving problems involving structural vibration, sound radiation from vibrating structures, sound in enclosed spaces, and propagation of sound and vibration.

1

Basic Concepts and Acoustic Fundamentals

1.1 Introduction

This book is intended to address the fundamental concepts that underpin the theoretical analyses of problems involving sound radiation from vibrating structures and the propagation of the generated sound through air. Sound generated as a result of aerodynamic sources (such as propellers and aircraft wings moving through the air) and sound propagation in the ocean are not discussed here, as these topics are extensive and are discussed in detail in many excellent books.

The aim of conducting a vibroacoustic analysis of any system is generally to determine the system response due to excitation by known forces or to find the relative magnitudes of subsystem responses caused by arbitrary exciting forces. Examples include the vibration response of aircraft and rockets to estimated excitation forces and the acoustic response of enclosures excited by an attached structure, including a partition separating the two enclosures. There are two fundamentally different approaches used in these analyses. The first is known as a ‘wave’ approach in which it is assumed that the subsystem being considered is semi-infinite in nature so that the amplitudes of any waves reflected back to the source of excitation (energy source) are negligible compared to the amplitudes of non-reflected waves. The second approach is known as a ‘modal’ approach in which the subsystem is small enough that reflected waves have a significant amplitude. In this case the system response is described in terms of its normal modes of vibration. The vibration can be either structural, where a solid structure vibrates, or an enclosed space where the air in the enclosure vibrates to produce sound.

The starting point for fundamental analyses in acoustics is usually the wave equation. The derivation and application of this equation is discussed at length in this chapter, following the discussion of some basic concepts such as acoustic field variables, mean square quantities, decibels, addition of incoherent sounds, subtraction of incoherent sounds, sound pressure magnitudes, speed of sound, dispersion and basic frequency analysis. Understanding these fundamental concepts is an important prerequisite to following the subsequent...